1. Field of the Invention
The present invention relates to the field of data recording and playback. More particularly, it relates to improvements in methods and apparatus for quickly identifying various key characteristics of a data storage disk presented to a disk utilization device, typically a disk drive, so that such device may operate on the disk accordingly.
2. Discussion of Prior Art
It is known in the art to house a data storage disk, e.g., an optical or magneto-optical disk, in a protective package so that the relatively delicate recording surfaces of the disk cannot be touched or otherwise physically damaged during periods of non-use. For example, in the commonly assigned U.S. Pat. No. 4,819,114 there is disclosed a data storage disk assembly in which a two-sided data storage disk is releasably supported at its periphery within a circular aperture defined by a rectangular frame, referred to as a disk "carrier." During periods in which the disk is not used, the carrier and its associated disk are contained in a box-like "caddy" which totally surrounds the carrier and prevents any inadvertent contact with the disk. When it is desired to use the disk, the caddy is inserted into a disk-utilization device, such as the disk drive or disk library disclosed in commonly assigned U.S. Pat. Nos. 4,773,058 and 4,817,071, respectively. In loading a disk into a disk library of the type disclosed in the '071 patent, the caddy is presented to the entrance of a carrier-unloading station, whereupon the caddy is grasped and advanced to a point at which a pair of fingers enter the caddy through a pair of spring-loaded doors located at the caddy's forward end and grasp the carrier within. Thereafter, the caddy is advanced in the reverse direction, the result being that the carrier (and its disk) is withdrawn from the caddy. The carrier is the advanced along a predetermined path leading either directly to a disk drive unit, or to an empty slot in a rack which is adapted to house a multitude of similar carriers and their associated disks.
The above-mentioned data storage disk assembly is illustrated in FIGS. 1 and 2 of the attached drawings. In FIG. 1, the disk assembly 4 is shown in combination with a disk utilization device 2 having an opening 2a for receiving the disk assembly. The disk assembly basically comprises a data storage disk 6, a disk carrier 8 and a caddy 10. As indicated above and shown in FIG. 2, the carrier comprises a planar frame 12 which defines a generally circular aperture 13 slightly larger than the disk. A pair of spring-loaded latches 14 cooperate with a disk-edge support 16, formed in the aperture-defining wall of the carrier, to releasably support the disk at its peripheral edge within the carrier's aperture. The disk carrier is also provided with certain cut-outs C and notches N in its leading and trailing edges, as determined by the direction in which the carrier is inserted into the disk drive. These cut-outs and notches cooperate with certain carrier-grasping and locating structure within the disk drive to extract the carrier from the caddy and to precisely locate the carrier within the drive.
Important to note in the disk carrier shown in FIG. 2 is that the carrier frame is provided with a pair of spaced holes, H and H', in the vicinity of the forward (or trailing) edge of the disk carrier. These holes serve as the indicia by which the disk drive, through suitable photoelectric sensors within the disk drive, determines whether or not the recording surfaces of the disk are write-protected. The disk user may selectively cover either or both of these holes by moving either or both of a pair of slidably-mounted tabs 18 (which are slidably mounted on the carrier frame) from a position in which a hole is exposed and, hence, detectable, to a position in which such hole is covered and, hence, not detectable. In FIG. 2, both of these holes are shown as being covered by tabs 18, indicating that both recording surfaces are write-protected. As disclosed in the aforementioned '114 patent, the disk user may change the coveting/non-coveting position of the write-protect tabs while the carrier is located within the caddy by sliding either of a pair of write-protected status indicators 20, 20' (shown in FIG. 1) which are slidably mounted on the end wall 10a of the caddy. These status indicators engage the write-protect tabs 18 when the carrier is safely positioned in the caddy, and sliding movement of the status indicators effects a corresponding movement of the write-protect tabs.
In a commercial version of this disk carrier described above, a third hole H" is located in the vicinity of the carrier edge opposite the write-protection holes. This third hole, which is provided by the disk manufacturer and is not alterable or coverable by the disk user, is sensed photoelectrically by the disk drive to determine the orientation of the disk and carrier in the drive, i.e., side A or side B of the disk facing upwards. It should be noted that, in the type of disk assembly discussed herein, the carrier and an associated disk are forever married and, though the disk may be temporarily separated from the carrier for use, it is always returned to the same carrier and in the same orientation.
As may be appreciated from the symmetry of the disk carrier shown in FIG. 2, the carrier may be received by the disk drive in any one of four different orientations, viz., side A facing upwards with carrier end 8A entering the drive first; side A facing upwards with end 8B entering the drive first; side B facing upwards with end 8A entering first; and side B facing upwards with end 8B entering first. In a disk library of the type disclosed in the afore-mentioned U.S. Pat. No. 4,787,074, it is necessary for a carrier to have this four-orientation symmetry since the library is adapted to (a) flip a carrier end-for-end, i.e. about axis X shown in FIG. 2, in order to present either of its two recording surfaces to the disk drive, and (b) insert a carrier into a disk drive with either of the two ends 8A or 8B leading. In order to detect which of the four orientations is present and whether or not the recording side presented is write-protected, the prior art disk drive includes a plurality optical sensors. These sensors are located at various positions within the disk drive to sense the aforementioned holes H, H', H", in the carrier after the carrier has been fully inserted and seated in the disk drive housing.
In the above system for identifying various features or characteristics of a data storage disk, it will be appreciated that the number of sensors in the disk drive is determined by the number of disk features (and the corresponding number of holes or indicia) to be sensed. The number of sensors may be as few as two, or may be as many as eight or more, as would be the case if it were desirable to detect additional features of the disk, such as disk type, storage capacity, etc. In addition to requiring a relatively large number of sensors, the prior art disk drives are disadvantageous in that the feature-identifying indicia on the carrier cannot be read until the carrier has been fully inserted and captured by the drive. This requirement slows down the start-up process.